Engine load control

ABSTRACT

This disclosure pertains to an engine load control which combines mechanical and fluid control devices whereby continuously to monitor and modify an engine load in conformance with an engine speed governor setting and fuel demand. A valve actuating bridge is suspended in a frame by cam following means riding on separate speed and fuel cams. At least one of the cams comprises adjustable segments whereby the response of the bridge may be matched with an engine speed-fuel relationship. The bridge actuates a two-stage spool-valve which permits sequentially a large flow of fluid followed by a relatively small flow of fluid into a linear actuator; this two-stage valving permits rapid response to sudden load changes followed by a slow stabilization or return to equilibrium without hunting. The linear actuator operates a pressure varying control valve in a pneumatic control circuit. The speed cam is actuated by a pneumatic positioning linear actuator and the fuel cam is actuated by the fuel rack of an engine speed control governor. An illustrated application of my invention is variation of blade pitch in a reversible controllable pitch propeller. Blade pitch is changed by a hydraulic servo-mechanism; the servo-mechanism is controlled by a pneumatic circuit having a single lever control, a pair of pressure regulating relay valves, and a double-acting selfcentering positioning linear actuator. Blade pitch is operatively determined by the lesser of the pressures established by the single lever control and the pressure varying control valves actuated by the engine load control.

United States Patent [191 Kobelt July 30, 1974 ENGINE LOAD CONTROL [76] Inventor: Jack R, Kobelt, 6110 Oak St.,

Vancouver 13, British Columbia, Canada 22 Filed: Aug. 28, 1972 21 Appl. No.: 283,904

Primary Examiner William L. Freeh Assistant Examiner-Robert E. Garrett [57] ABSTRACT This disclosure pertains to an engine load control which combines mechanical and fluid control devices whereby continuously to monitor and modify an engine load in conformance with an engine speed governor setting and fuel demand. A valve actuating bridge is suspended in a frame by cam following means riding on separate speed and fuel cams. At least one of the cams comprises adjustable segments whereby the response of the bridge may be matched with an engine speed-fuel relationship. The bridge actuates a twostage spool-valve which permits sequentially a large flow of fluid followed by a relatively small flow of fluid into a linear actuator; this two-stage valving permits rapid response to sudden load changes followed by a slow stabilization or return to equilibrium without hunting. The linear actuator operates a pressure varying control valve in a pneumatic control circuit. The speed cam is actuated by a pneumatic positioning linear actuator and the fuel cam is .actuated'by the fuel rack of an engine speed control governor. An illustrated application of my invention is variation of blade pitch in a reversible controllable pitch propeller. Blade pitch is changed by a hydraulic servomechanism; the servo-mechanism is controlled by a pneumatic circuit having a single lever control, a pair of pressure regulating relay valves, and a double acting self-centering positioning linear actuator. Blade pitch is operatively determined by the lesser of the pressures established by the single lever control and the pressure varying control valves actuated by the engine load control.

, ll Claims, 10 DrawingFigures PATENTEDJULSUIBH sum 1 [IF ENGINE LOAD CONTROL This invention relates to novel improvements indevices which are known in the art to which they pertain as engine load controls, or to devices which automatically and continuously monitor and modify an engine load whereby to match engine load with engine speed for optimum performance in internal combustion engines, or to loadcompensators which belong to or are of the general characterof engine load controls. In its simplest form, an engine load control receives engine speed setting and fuel demand information and produces a load maintaining or modifying signal. Normally, the engine speed information eminates from a throttle control which alsodetermines the speed setting in a speed controlling governor, and the fuel demand information originates at the fuel rack of the governor. The load maintaining or modifying signal may be transmitted to the engine loading device by either electric, mechanical, or pneumatic control circuitry, devices, and servo-mechanisms.

The performance of internal combustion engines is normally described by a speed-fuel comsumption correlation. A speed control governor will act to maintain a speed setting providing more or less fuel depending on the engine load. If the fuel demand is greater than the optimum determined by the speed-fuel correlation, then the engine is overloaded and may be damaged; if the fuel demand is less than the optimum, then the engine is operating inefficiently.

A case where it is desirable to modify engine load to suit engine speed is in marine propulsion systems. In the case of tugboats, where operating conditions may vary from loaded to unloaded, heavy swell to calm seas, high winds to no wind, and open water towing to harbor manoeuvering, itclearly is desirable to be able to modify the propulsion system load on the tugboat engine in accordance with operating conditions. It is for these reasons that variable pitchor controllable pitch propellers have been developed. ln the application of my invention to controllable pitch propellers, the engine load control operates a servo-mechanism which in turn modified the propeller pitch, thereby altering the engine load to suit a given engine speed throttle setting.

Further,in general but with specific reference to the controllable-pitch propeller application, it is undesirable that an engine load control vacillate or hunt for an equilibrium position. On the other hand, it is essential that the engine load control respond quickly to sudden changes in conditions such as when a tugboat endeavorsto accelerate quickly, noses hard into a push, or comes uphard against a towline. It will be evident to one skilled in this art that a quick load control response normally involves loose control and, consequently, hunting of the control. It is for this reason that I have in my invention provided novel two-stage spool-valving means which provide large fluid flow and large adjust means whereby elements in a control system may be actuated manually to compensate for failure of other elements in the system. In the event of throttle, load control, or governor failure, my invention is provided with a mechanical overriding means whereby a fixed load may be placed on the engine.

Therefore, it is one object of my invention to provide an engine load control which combines mechanical and fluid control devices whereby to receive engine speed and fuel demand information and produce a load modifying signal.

It is another object of my invention to provide an engine load control which provides a rapid response to sudden changes in load followed by a slow return to equilibrium without hunting.

It is yet another object of my invention to provide an engine load control having a means whereby variations in engine, control system, servo-mechanism, and linkage characteristics may be calibrated out of the engine load control system through an actuator cam whose shape is made up of adjustable segments.

. Still another object of my invention is to provide an engine load control having a mechanical means whereby the engine load control may be manually overridden to produce a fixed engine load.

Yet another object of my invention is to provide an engine load control whose load modifying signal may be used to actuate either fluid control or electric control devices in a load control circuit.

Still another object of my invention is-to provide an engine load control wherein the load control signal is produced by a fluid powered linear actuator, the lubrication system of the engine being controlled providing trolled.

A further object of my invention is to provide an en gine load control which can be used in combination with control circuitry and servo-devices to vary the blade pitch on a controllable pitch propeller whereby to compensate for both sudden an gradual engine load changes.

Still further objects and advantages of the present invention reside in the details of construction of the embodiment of the invention disclosed herein.

These and further objects of the invention will be evident from the study of the following disclosure and the accompanying drawings which illustrate improved details of construction of a preferred embodiment of the invention. This embodiment is merely exemplary and is not intended to detract from the full scope of the invention as set out in he annexed claims.

In the drawings, wherein like numerals refer to like parts:

FIG. 1 is a plan view of an engine load control assem bly in accordance with my present invention;

FIG. 2 is a frontal view of the assembly taken substantially along line 2-2 in FIG. 1';

FIG. 3 is a partial sectional plan view of the assembly taken substantially along line 3-3 in FIG. 2;

FIG. 4 is a partial sectional elevation of the assembly taken substantially along line 4-4 in FIG. 3;

FIG. 5 is a partial sectional view of the assembly taken substantially along line 5-5 in FIG. 4;

FIG. 6 is a partial sectional view of the assembly taken substantially along line 6-6 in FIG. 4;

FIG. 7 is a sectional view of an adjustable cam segment taken substantially along line 7-7 in FIG. 4;

FIG. 8 is a view of an adjustable cam segment taken substantially along line 8-8 in FIG. 7;

FIG. 9 is a partial sectional elevation of a linear actuator and two-stage spool-valve taken substantially along line 9-9 in FIG. 4;- t

FIG. 10 is a schematic arrangement wherein my invention is shown in combination with a reversible con trollable pitch propeller, engine, governor, a pair of pressure regulating relay valves, a double-acting selfcentering linear actuator, and a single lever control.

Turning now to the drawings, FIGS. 1 and 2 show a plan and elevation of my invention wherein frame means 21. encloses and supports a control mechanism generally denoted by the numeral 22. Mounted on the top of frame means 21 is bracket 23 to which is attached pressure varying control valve 24. Pressure varying control valve 24 is of the type where fluid from an energizedfluid source enters at port 25, enters a control circuit at port 26, and exhausts at port 27; the pressure at port 26 is proportional to the depression of value-spool 28, is adjustable by spring means and setting screw 29, and may be no higher than that at port 25. While many variations in linkage and mounting are possible, in the embodiment of my invention here disclosed lever 30 is pivotally mounted in bracket 23 by means of pin 31 whereby extension of actuator rod 32 from linear actuator 33 within frame 21 causes a depression of valve spool 28. Manual overriding means, comprising nut 34 and screw 35 threaded into member 36 of bracket 23, is provided whereby valve spool 28 may be depressed a desired amount by turning screw 35 against lever 30 and locking it in place with nut 34.

Pivotally mounted in frame 21 are speed cam shaft 37 and fuel cam shaft 38. Secured to shaft 37 is speed actuator lever 39 having hole 40 for output linkage to a machanically actuated engine speed control governor. Secured to shaft 38 is fuel-rack actuated lever 41 having hole 42 for input linkage from the fuel-rack of an engine speed control governor..Frame means 21 is provided with foot members 43 and 44 having mounting holes 45. v

FIGS. 3, 4, 5 and 6 show details of the engine load control mechanism 22 enclosed within frame means 21. Secured to speed shaft 37 is engine speed cam means 46 comprising hub 47 and cam contour plate 48. Secured also to shaft 37 is actuator lever 49 pivotally interconnected to one end of link 50 by means of pin 51. The other end of link 50 is pivotally interconnected to rod portion 52 of fluid operated linear actuator 53 by means of pin 54. FIG. 3 shows the details of linear actuator 53 wherein rod 52 is secured to piston 145; energized fluid entering chamber 55, formed between piston 145 and cylinder portion 55, through port 91 overcomes the force of spring 57 on piston 145,

thereby causing rod 52 to extend in direction-58. Referlishes, via valve 128, a pressure at port 91 of the load I control representative of a desired speed setting for the engine. The position of engine speed cam 46, is therefore, representative of the desired engine speed setting to be maintained. It should be clear that fluid pressure in chamber 55 and extension of rod 52 cause speed cam 46 to pivot in direction 60; exhausint fluid from chamber 55 will cause spring 57 to retract rod 52 and cam 46 to rotate in direction 59. One end of speed cam follower link 61 is pivotally connected to frame 21 by means of pin 62 and ear 63; the other end of link 61 is pivotally connected to one end of three-role bridge link 64 by means of pin 65. Rotatably mounted on pin 65 is cam follower roller 66. Pivotally connected to the other end of link 64 is speed-end 77 of bridge 67 by means of pin 68 and stabilizing link 69 by means of pin 70. Sway link 69 is pivotally connected to frame 21 by means of pin 146 and ear 147. It should be clear that when cam 46 pivots, cam follower 66 will cause link 64 to raise and lower speedend 77 of bridge 67 in accordance with the movement and contour of cam 46.

Secured to shaft 38 is engine fuel cam means 71 comprising cam plate 72, hub 73, cam segments 74, washers 75 and bolts 76. Cam follower link 78 is pivotally mounted at one end in frame 21 by pin 79 and ear 80. The other end of link 78 is pivotally connected to one end of two-hole link 81 by means of pin 82. Rotatably mounted on pin 82 is cam follower roller 83. The other end of link 81 is pivotally connected to the fuel-end 84 of bridge 67 by pin 85. Lever 41 being secured to shaft 38 and linked to the fuel rack of a speed control governor, or otherwise being pivoted in proportion to the fuel demand of an engine, clearly shaft 38 will cause cam 71 to pivot with lever 41. Cam follower 83 will follow the contour of cam 71 as the latter is pivoted, thus raising and lowering end 84 of bridge 67 in accordance with the movement and contour of cam 71. Referring to FIG. 10, movement of comtrol lever 136 establishes, via valve 128, a pressure at port 140 of governor 123 representative of the desired engine speed setting. Governor 123 acts in a conventional manner to compare the desired engine speed setting with the actual engine speed, and position the governor fuel-rack to maintain the speed setting. The governor demanded fuel signal is supplied, via lever 125 and link 124, to position the fuel cam means 71.

It should be evident from the foregoing description of the operation of earns 46 and 71 that pivotal movement of either cam will upset the position of bridge 67. It should however be noted here that whereas increased throttle pressure resulting in increased speed has been shown to rotate cam 46 in direction 60, there to maintain equilibrium the increased engine fuel demand established by a governor should be transmitted to fuel link 41 and 71 so as f0 move the fuel end of bridge 67 in a direction opposite to that caused by movement of cam 46. That is, raising of bridge end 77 with increased speed should cause a falling of bridge end 84 with increased speed, for a substantially constant load. Put another way, if cams 46 and 71 both pivot in the same direction with increased or decreased engine speed, then the contours of both cams must vary radially in substantially the same way; conversely, if the pivotal directions of cams 46 and 71 are opposite for increased or decreased engine speed, then their contours must be substantially a mirror image of each other.

With reference to FIGS. 7 and 8 it can be seen that the shapes of at least one cams 46 and 71 may be altered for fine calibration adjustments to account for variations of speed-fuel characteristics of a given engine. Cam segment 74 has an oversize hole 86 which permits movement of each segment with respect to cam plate 72. Once the desired location of each segment is obtained, bolts 76 and washers 75 are tightened.

Looking now at FIG. 9, it will be seen that linear actuator 33 and two-stagespool-valve 87 share an integral housing 88. Linear actuator 33 comprises cylinder portion 89, piston portion 90, rod portion 32, spring 92, and seal 93. Spool-valve 87 comprises body 94, spool 95, fluid supply port96, needle valve 97, and spool spring 98. Spring 98 and bridge 67determine the position of spool 95 in valve body 94. Spool 95 comprises rapid flow valve portion 99 and recess 100, reduced flow valve portion 101 and recess 102, flow duct 103, and duct ports 104 and 105. To obtain two-stage spool-valving, it should be noted that recess 100 must be of a length whereby duct 119 and port 107 are not open at the same time. Fluid entering the system at port 96 flows out of or into chamber 106 of linear actuator 33, through either or both of ports 104 and 105, depending on the position of spool 95. When bridge 67 drops and spring 98 extends spool 95, then fluid from chamber 106 is dumped through ports 104 and 107; when bridge 67 rises so as to compress spring 98 and depress spool 95, then fluid flows into chamber 106 through ports 104 and 105; when bridge 67 and spring 98 maintain spool equilibrium, then fluid passes only through needle valve 97 and port 105 into-chamber 106, through vent hole 108 and exhaust port 109. Fluid dumped through ports 107 and 109 into frame 21 is drained off to a sump through port 110 in frame 21.

With reference now to FIGS. 1 through 9, consider 1 the operation of my invention. Commencing with a stable equilibrium condition where engine speed is substantially constant, cam 46 is held fixed by linear actuator 53 through link and lever 49; therefore end 77 of bridge 67 remains substantially stationary. An increase in load on an engine whose governor speed setting is substantially constant will cause the governor to demand more fuel for the engine. A demand for more fuel will be transmitted to cam 71 by means of lever 41 and shaft 38, causing cam 71 to pivot in direction 111 and end 84 of bridge 67 to drop. When the portion of bridge 67 in contact with spool 95 drops, spool 95 moves in direction 112. Needle valve port 113 is closed off by spool portion 101 and port 107 is opened to recess 100, thus permitting fluid from chamber 106 to flow through spool duct 103 and out of ports 104, 107 and 110. Removal of fluid from chamber 106 causes piston 90 and rod 92 to drop in direction 115; this movement of rod 32 is transmitted through electric, pneumatic, or mechanical means, devices, circuitry and servo-mechanisms, as required to implement a reduction in engine load. As the engine load is reduced, speed still being held constant, the engine fuel demand determined by the governor drops; this reduced fuel re quirement is transmitted, as was the demand for more fuel, to cam 71 causing it to pivot in direction 116 and end 84 of bridge 67 to rise, carrying spool 95 with it in direction 117. Portion 101 of spool 95 thus closes off port 107, duct 113 of needle valve 97 is re-opened and spool 95 slowly returns to equilibrium position where the'flow of fluid through needle valve 97, port 105, and spool duct 103 equals that through piston hole 108, and exhaust ports 109 and 110. Hence, upon receiving increased fuel demand information at cam 71, my invention has rapidly dropped the engine load through a high dumping flow rate of fluid from chamber106, through ports 104 and 107, followed by a slow return to equilib rium at a lower engine load by means of restricted fluid flow through needle valve 97 and piston hole 108.

Consider now a drop in load at a fixed engine speed. Cam 46 is held fixed by linear actuator 53, as in the case of increased load. A demand for less fuel originating at the engine governor is transmitted to cam 71 by lever 41 and shaft 38, causing cam 71 to pivot in direction 116 and raising end 84 of bridge 67. Spool 95 is raised in direction 117, thus opening ports 104 and 105 to fluid flow into chamber 106 and raising piston and rod 32 in direction 118. This upward movement of rod 32 is transmitted by means, as described in the previous example, whereby to increase the engine load. As the engine load increases, the fuel demand increases, thus dropping end 84 of bridge 67 and causing spool portion 99 to close off duct 119 and spool to drop slowly until equilbrium is again achieved such that the flow of fluid through needle valve 97 andport is equal to that through hole 108 in piston 90. Thus, it is seen that the engine load is increased in two steps: a rapid stage by fluid flow through duct 119 and port 104 and a gradual stage by flow through duct 113 and port 105.

I It can be shown in view of the foregoing load increase and decrease, at a fixed engine speed, that a change of speed at a constant fuel demand will cause movement of spool 95 in either direction 112 or 117; such a case is normally only of academic interest inasmuch as engine speed is the independent and fuel the dependent variable with conventional .engine speed governors. However, a rapid change in speed is expected to entail a deviation from the optimum speed-fuel correlation, depending on the characteristics of the engine loading device, thus requiring an adjustment in engine load as described above in the case of load change at constant engine speed. Therefore it will be clear to one skilled in the art that for every engine speed and fuel demand there exists a distinct geometric configuration relating earns 46 and 71, bridge 67, spool 95 and rod 32.

Calibration of my invention may be achieved in the following way. Whereas secondary effects of fluid viscosity may in some cases be ignored, a stable operating temperature should be achieved. if the fluid operating linear actuator 33 is supplied by an engine lubrication system, then the engine should be allowed to reach normal operating temperature prior to calibration of the engine load control. For a given engine load and speed, the correct fuel demand determined by a speed-fuel correlation for the engine and established by a speed governor which determines the angular position of cam 71, cam segment 74 under cam follower roller 83 should be adjusted so as to make the position of piston 90 and rod 32 conform with the appropriate engine load. Engine speed should be varied stepwise, thus changing the position of cams 46 and 71 together whereby each of cam segments 74 may be properly adjusted.

Turning now to an application of my invention in combination with an engine and a load varying device,

FIG. 10 illustrates an engine 120 coupled by shaft 121 to a reversible and controllable pitch propeller 122. Fuel cam 71 of my engine load control 21 is interconnected to the fuel-rack of governor 123 by means of lever 41, link 124, and governor lever 125. Pressure varying control valve 24 of engine load control 21 is duct connected in a pneumatic control circuit with a single lever control 126 having three pressure varying control valves 127, 128, and 129 respectively controlling forward pitch, throttle, and reverse pitch, a pair of pressure regulating relay valves 130 and 131, and a double-acting self-centering positioning linear actuator 132. Servo-mechanism 133 normally includes a hydraulic fluid power source, valving, and a linear actuator; in conventional controllable pitch propeller, it is normally incorporated, at least in part, in either propeller hub 134 or coupling 135.

Movement of control lever 136 in direction 137 actuates valves 127 and 128, creating forward pitch in propeller 122; movement of lever 136 in direction 138 actuates valves 1 28 and 129, creating reverse pitch in propeller 122. Assuming forward pitch, pressure at port 139 of valve 130, as determined by valve 127, is established at a certain level for a given maximum allowable. pitch corresponding to the throttle setting of valve 128. Pressure at port 140 of governor 123, as established by valve 128, determines a speed setting for engine 120. The fuel-rack of governor 123 determines the position of lever 41 and cam 71; pressure at port 91 of engine load control 21 determines the position of cam 46. Hence, speed and fuel demand information are fed into engine load control 21 in manner consistent with the previous description of the structure and operation of my invention. Now, the actual blade pitch in propeller 122 will be determined by the pressure at port 141 of position 132. This pressure will be less than or equal to the pressure at pilot port 142 of valve 130; the pressure at port 142 is determined by engine load control 21 actuating valve 24. Therefore, whereas single-lever control 126 determines the maximum attainable pressurein positioner 132 and, hence, maximum allowable blade pitch at a given throttle setting, load control 21 reducesthis pressure and the blade pitch if the engine becomes overloaded. Likewise it can be shown that valves 128, 129, 131, and 24 control posicam following means to said engine speed cam means tioner 132 and blade pitch in the reverse pitch operatthe spirit of my invention. Therefore, it is my intention that no limitations be implied and that the hereto annexed claims be given the broadest interpretation to which the language fairly admits whereby to cover all changes, modifications, and equivalents as may fall within the true scope of my invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

and fuel cam means, two-stage spool-valve means interconnected to said bridge means, linear actuator means operatively connected by said two-stage spool-valve means to an energized fluid source, said engine load varying means interconnected to said linear actuator means, whereby a change in pivotal position of either said engine speed cam means or fuel cam means extends or retracts said linear actuator means thereby altering said engine load.

2. An engine load control system as defined in claim 1 wherein at least one of said engine speed cam means and said engine fuel cam means includes a plurality of cam segments mounted on a cam plate, said cam segments adjustable whereby to accommodate an engine speed-fuel relationship of said engine.

3. An engine load control system as defined in claim 1 wherein said energized fluid source is the lubrication system of said engine controlled by said engine load control.

4. An engine load control system as defined in claim 1, wherein said engine load varying means includes a second fluid pressure source, a fluid pressure varying valve operatively connected to said second fluid source to generate a fluid pressure signal as a function of the position of said fluid pressure varying valve, said pressure varying valve actuated by said linear actuator means, whereby said fluid pressure signal is varied by said linear actuator means to alter said load.

5. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected to a fluid powered linear actuator, said fluid powered linear actuator inter-connected through a throttle control means to a fluid power source, said throttle control means providing said engine speed signal, said engine fuel cam means pivotally interconnected to a fuel control of an engine speed control governor, said speed control governor providing said engine fuel signal.

6. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected to a speed control of an engine speed control governor, said engine speed control governor providing said engine speed signal.

7. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected by a mechanical linkage to a throttle control means, said throttle control means providing said engine speed signal.

8. An engine load control system as defined in claim 1 wherein said engine load varying means includes an emergency mechanical overriding means.

9. An engine load control system as defined in claim 1 wherein said engine load varying means includes a pneumatic pressure varying valve actuated by said lincar actuator means and operatively connected to a servo-device, said servo-device operatively altering blade pitch in a controllable pitch propeller.

10. An engine load control system as defined in claim 1 wherein said engine load varying means comprises in combination, a pneumatic pressure varying control valve actuated by said linear actuator means and ductconnected to the pilot ports of a pair of pneumatic pressure regulating relay valves, a single lever control having a pneumatic pressure varying control valve duct-connected to each of said pneumatic pressure regulating relay valves, one of said pneumatic pressure regulating relay valves duct-connected to each end of a double-acting self-centering positioning linear actuator, said positioning linear'actuatoroperatively connected to a hydraulic servo-mechanism, said hydraulic servo-mechanism operatively connected to a reversible controllable pitch propeller.

11. An engine load control system comprising in combination an engine, engine load, engine load varying means operatively connected to said engine load, and an engine load control operatively connected to said engine load, said engine load control comprising a frame means, engine speed cam means pivotally mounted in said frame means, engine fuel cam means pivotally mounted in said frame means,'valve actuating bridge means suspended from said frame means and interconnected by cam following means to said engine speed cam means and fuel cam means, two-stage spoolvalve means interconnected to said bridge means, fluid operated linear actuator means operatively connected by said two-stage spool-valve means to an energized fluid source, said engine load varying means including a pneumatic pressure varying control valve interconnected to said linear actuator means, said engine speed cam means pivotally interconnected to a fluid operated positioning linear actuator, said positioning linear actuator being actuated by a fluid control desired engine speed signal, said engine fuel cam means being actuated pivotally by an engine fuel signal from a fuel-rack of an engine speed control governor, whereby a change in pivotal position of either of said engine speed cam means or fuel means extends or retracts said linear actuator means thereby actuating said engine load varying means and altering said engine load. 

1. An engine load control system comprising in combination an engine, engine load, engine load varying means operatively connected to said engine load, and an engine load control operatively connected to said engine load, said engine load control comprising a frame means, engine speed cam means pivotally mounted in said frame means, a desired engine speed signal pivotally actuating said engine speed cam means, engine fuel cam means pivotally mounted in said frame means, an engine fuel signal pivotally actuating said engine fuel cam means, valve actuating bridge means suspended from said frame means and interconnected by cam following means to said engine speed cam means and fuel cam means, two-stage spool-valve means interconnected to said bridge means, linear actuator means operatively connected by said two-stage spool-valve means to an energized fluid source, said engine load varying means interconnected to said linear actuator means, whereby a change in pivotal position of either said engine speed cam means or fuel cam means extends or retracts said linear actuator means thereby altering said engine load.
 2. An engine load control system as defined in claim 1 wherein at least one of said engine speed cam means and said engine fuel cam means includes a plurality of cam segments mounted on a cam plate, said cam segments adjustable whereby to accommodate an engine speed-fuel relationship of said engine.
 3. An engine load control system as defined in claim 1 wherein said energized fluid source is the lubrication system of said engine controlled by said engine load control.
 4. An engine load control system as defined in claim 1, wherein said engine load varying means includEs a second fluid pressure source, a fluid pressure varying valve operatively connected to said second fluid source to generate a fluid pressure signal as a function of the position of said fluid pressure varying valve, said pressure varying valve actuated by said linear actuator means, whereby said fluid pressure signal is varied by said linear actuator means to alter said load.
 5. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected to a fluid powered linear actuator, said fluid powered linear actuator inter-connected through a throttle control means to a fluid power source, said throttle control means providing said engine speed signal, said engine fuel cam means pivotally interconnected to a fuel control of an engine speed control governor, said speed control governor providing said engine fuel signal.
 6. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected to a speed control of an engine speed control governor, said engine speed control governor providing said engine speed signal.
 7. An engine load control system as defined in claim 1 wherein said engine speed cam means is pivotally interconnected by a mechanical linkage to a throttle control means, said throttle control means providing said engine speed signal.
 8. An engine load control system as defined in claim 1 wherein said engine load varying means includes an emergency mechanical overriding means.
 9. An engine load control system as defined in claim 1 wherein said engine load varying means includes a pneumatic pressure varying valve actuated by said linear actuator means and operatively connected to a servo-device, said servo-device operatively altering blade pitch in a controllable pitch propeller.
 10. An engine load control system as defined in claim 1 wherein said engine load varying means comprises in combination, a pneumatic pressure varying control valve actuated by said linear actuator means and duct-connected to the pilot ports of a pair of pneumatic pressure regulating relay valves, a single lever control having a pneumatic pressure varying control valve duct-connected to each of said pneumatic pressure regulating relay valves, one of said pneumatic pressure regulating relay valves duct-connected to each end of a double-acting self-centering positioning linear actuator, said positioning linear actuator operatively connected to a hydraulic servo-mechanism, said hydraulic servo-mechanism operatively connected to a reversible controllable pitch propeller.
 11. An engine load control system comprising in combination an engine, engine load, engine load varying means operatively connected to said engine load, and an engine load control operatively connected to said engine load, said engine load control comprising a frame means, engine speed cam means pivotally mounted in said frame means, engine fuel cam means pivotally mounted in said frame means, valve actuating bridge means suspended from said frame means and interconnected by cam following means to said engine speed cam means and fuel cam means, two-stage spool-valve means interconnected to said bridge means, fluid operated linear actuator means operatively connected by said two-stage spool-valve means to an energized fluid source, said engine load varying means including a pneumatic pressure varying control valve interconnected to said linear actuator means, said engine speed cam means pivotally interconnected to a fluid operated positioning linear actuator, said positioning linear actuator being actuated by a fluid control desired engine speed signal, said engine fuel cam means being actuated pivotally by an engine fuel signal from a fuel-rack of an engine speed control governor, whereby a change in pivotal position of either of said engine speed cam means or fuel means extends or retracts said linear actuator means thereby actuating said engine load varying means and altering said engine load. 